US 3843420 A
Description (OCR text may contain errors)
oct. 2v2, 1974 Filed' Oct. 24. 1972 yoox vo|..% Ni/ (vom/o Ni +voL./0 Fe) J.1,GITTLEMAN Erm. 3,843,420
SPUTTERED GRANULAR FERROHAGHETIC IRONNICKEL-SILICA FLHS 3 Sheets-Sheet 1 0t.22,1974 J.|.G1TTLEMAN n. 3,843,420
SPUTTERED GRANULAR FERROIAGNETIC IROHNICKEL-SILICA FILMSA Filed oct. 24. 1972 s sheets-snutz r Fig.2.
|00 x voL,% Ni/(voL./O -i+voL. %Fe) VOLUME Sio2 United States Patent O 3,843,420 SPUTIERED GRANULAR FERROMAGNETIC IRON-NICKEL-SILICA FILMS Jonathan Isaac Gittleman and Joseph John Hanak, Trenton, NJ., assignors to RCA Corporation Filed Oct. 24, 1972, Ser. No. 299,770 Int. Cl. C04b 35/ 00 U.S. Cl. 14S-31.55 10 Claims ABSTRACT OF THE DISCLOSURE Granular ferromagnetic films of an iron-nickel alloy `and silica made by radio frequency sputtering of a three component target. These materials are useful -for magnetic head applications. Compositions having high permeability and high resistivity are useful as integrated circuit inductor cores.
The invention hereindescribed was made in the course of or under a contract with the Government of the 'United States.
`GRANULAR FERROMAGNETIC FILM This invention relates to novel granular ferromagnetic lms. More particularly, this invention relates to granular feromagnetic films of iron, nickel and silica.
BACKGROUND OF THE INVENTION Granular ferromagnetic films, commonly referred t as ferromagnetic cermets, are mixtures of incompatible materials: a ceramic, which is an electrical insulator, and `a metal, which is a conductor. Ferromagnetic cermets have little solubility between the metallic phase and the ceramic phase at temperatures of preparation `and -thus are heterogeneous materials wherein small metal grains are embedded in an amorphous insulating matrix. As such, Ithe properties of such cermets, such as permeability and resistivity, generally vary directly with the relative proportion of -metal and insulator present in the composition. Cermets are of interest for magnetic head applications, integrated circuit inductor cores for TV circuits and lilters and the like.
Known cermets of silica, such as Ni(1 X)(SiO2)X and (Fe)1 ,(SiO2)x are not suitable for certain -applications such `as integrated circuit inductor cores because they have permeabilities which are too low for materials of sufficiently high resistivity. In particular, it is desirable to -be able to make an integrated circuit inductor core operating in the range 200-500 mHz. which has a resistivity greater than *3 ohms-cm. and a permeability in a range 30-40 or higher.
SUMMARY OF THE INVENTION We have found that granular ferromagnetic films of nickel, iron and silica combine desirable magnetic properties with high electrical resistivity. These materials have increasing resistivity with increasing silica content, as would be expected, but they have surprisingly high permeabilities even lat relatively low metal content. The films described herein are prepared by cosputtering iron, nickel and silica onto a suitable substrate in the desired amounts.
BRIEF DESCRIPTION OF 'THE DRAWINGS FIG. 1 is a graph of the contours of constant permeability for iron-rich iron/ nickel alloysilica cermets wherein ythe abscissa represents the silica concentration, given in volume percent, and the ordinate represents nickel c0ncentration in lthe nickel-iron alloy, given in volume percent.
3,843,420 Patented Oct. 22, 1974 DETAILED DESCRIPTION OF THE vINVENTION The granular ferromagnetic films hereinafter described have the composition wherein x is from 0.001 to 0.7 parts (0.1-70%) by volume and y is from 0.001 to 0.999 parts (0l-99.9%) by volume. These compositions vary from nickel-rich materials having high permeability and comparatively low resistivity, useful for low frequency applications in the range l-50 mHz. for cores of magnetic recording heads and linductors for TV circuits and filters, to iron-rich materials having high permeability and high resistivity useful in the range 10-1000 mHz. for thin film inductors for high lfrequency use yin TV tuners. Preferably, the nickel-rich compositions will contain from about 40 to about by volume of nickel in the nickel-iron alloy Iand 0.1 to about 30% `by volume of silica and the ironrich compositions will contain from about 1 to about 55% by volume of nickel in the nickel-iron alloy and from 2S-60% by volume of silica. Compositions containing 40-50% by volume of silica and 15-40% by volume of nickel in the nickel/iron alloy are particularly useful for integrated circuit cores which will operate in the 200- 500 mHz. range.
The above-described ferromagnetic films can be prepared 4by radio frequency sputtering in conventional manner onto a substrate from a target composed of sections of iron, nickel and silica. The nature of the substrate is not critical and can be of ceramic, metal, glass and the like.
The composition of the film deposited on the substrate depends on the target geometry. A continuously changing composition of the cermet can be sputtered onto the substrate, or, a uniform composition can be deposited. When a continuously -changing composition is desired to be deposited, a target can be prepared by cutting sheets of nickel, iron and silica, suitably from 1/16 to 1A inch thick, in the form of sections of a disk and the sections placed on the surface of a sputtering cathode.
When a uniform composition is desired to be deposited, a target can be prepared by mixing nickel, iron and silica powders in the proportions desired in the sputtered film, pressing the resultant mixture in the shape of a disk target and firing the disk at an elevated temperature, e.g., 1100 C., for about an hour in a hydrogen atmosphere. Alternatively, a suitable target can also be prepared by placing strips cut from sheets of two of the components in uniform manner onto a disk of the third component, e.g., placing strips of nickel and silica on an iron target.
Methods of sputtering are more completely described in a copending application of Hanak, Ser. No. 175,587 filed Aug. 27, 1971, now abandoned.
The relative amounts of each constituent of the present ferromagnetic films required on the target to give a film of the desired composition can be calculated from the relative sputtering rates according to the method described 1n aforementioned application, Ser. No. 175,587.
The ferromagnetic films can be employed as sputtered, but preferably are annealed at elevated temperatures which may serve to enhance the permeability. Annealing can be carried out by heating at temperatures of from about 200 C. up to the temperature which would adversely alfect the substrate. Temperatures of from about 225 to about 300 C. are suitable when using glass substrates.
The invention will Ibe further illustrated by the following examples, but it is to be understood that the invention is not meant to be limited to the details described therein.
In the examples, permeability was determined according to the following procedure, using a magnetic recording head containing a pair of windings, one for the record/ playback function and the other for the erase function. One of the windings was driven by a reference source of a phase-sensitive detector which measures the change in signal from the other winding when the head is contacted with the specimen. The signal is linearly related to the magnetic reluctance of that portion of the sample beneath the gas of the recording head. The reluctance is inversely proportional to nd., the product of permeability and thickness. If two standards are measured, the permeability at any point (x,y) of the sputtered film can be determined by the following equation:
no, indo, @fn-lemme [(fL d )"x-tzd )"1 *FWMV (517, 11)"AV2 l wherein AV (x,y) is the signal and the subscripts 1,2 refer to the standards.
Example I.-Preparation of a Film of Variable Composition A 6" diameter disk-shaped target was prepared from sheet material by fabricating into three sectors, one sector containing nickel, another iron and the third silica. The central angle subtended by each sector was 43, 180 and 137 respectively.
The target was placed as the cathode in a radio frequency sputtering system using argon at a pressure of about 10 microns and sputtered onto a glass substrate 4.5 x 4.5 inches placed parallel to the target and spaced about 2 inches therefrom.
The sputtered ilm varied in composition from about 5-40% by volume of nickel, l5-80% by volume of iron and -60% by lvolume of silica.
The magnetic permeability measurements are presented in the form of contours on the graph shown in FIG. l.
Referring now to lFIG. 1, the numbers on the graph are the permeability measurements, identifying the compositions which :gave such measurements. It is apparent that materials of particularly high permeability (about 130- 170) which would be expected to have high resistivity contained from about 40 to about 50% by volume of silica vand from about to about 40% by volume of nickel in the nickel/iron alloy.
The film was annealed under vacuum (2 107 mm. Hg) for two hours at 250 C. 'Ihe permeability was remeasured and it was found that for compositions having an initially low permeability, a small increase in permeability was noted after annealing. However, compositions having a high permeability initially had a greater increase in permeabilty after annealing. The composition (FegmNimg)0 54(Si02)0.46 having an initial peak at about 170 had a permeability after annealing of 310.
Example 2.-Preparation of a Film of Variable Composition The procedure of Example 1 was followed except substituting a target wherein the angles subtended by the nickel, iron and silica sectors were 151, 72 and 137, respectively.
The resultant ilrn varied in composition from about 20-85% by volume of nickel, 5-.40% by volume of iron and 10-55% by volume of silica.
The magnetic permeability was recorded in the form of contours. The results are given in FIG. 2.
Referring now to FIG. 2, materials having high permeability will have compositions in the range 40-65% by volume of nickel in the nickel/ iron alloy and 13-20% by volume of silica.
Example 3 The resistivity in ohms-cm. of the iilms prepared in Examples 1 and 2 was measured by replacing the recording head used to determine permeability with a conventional 4 point probe. Resistance of the composition as a function of its position on the film was measured using a Direct Current supply in conjunction with a digital voltmeter. The outline of areas having constant resistivity are shown in FIGS. 3 and 4, wherein the resistivity measurements are shown on the graphs. FIG. 3 is a graph of the resistivity measurements of the lrn prepared in Example l and FIG. 4 is a graph of the resistivity measurements of the lm prepared in Example 2.
The lilms were annealed under vacuum (2 10'I mm. Hg) for two hours at 250 C. and resistivity remeasured. Resistivity of most of the compositions had increased by about 25% Example 4,--Preparation of a Film of Constant 4Composition A target was prepared by admixing powders of iron, nickel and silica in a ratio by weight of 1:0.531 :0.336 respectively. The mixture was pressed at 12,000 p.s.i. into the shapes of a disk six inches in diameter and about 1A inch thick. The disk was tired at 1100 C'. for one hour in hydrogen.
The resultant sputtered film had the composition in parts by volume. The permeability was and resistivity was 9 1O2 ohms-cm. The lilm was annealed at 250 C. for two hours under vacuum and cooled to room temperature. The permeability had increased to 270 and resistivity was 1.1 X l0*1 ohms-cm.
Example 5.-Preparation of a Film of Constant Composition A target was prepared by laying strips of silica 1A inch wide onto an iron disc in regularly spaced rows d inch apart. Nickel squares 1A x 1A: inch were placed between the silica strips about one inch apart.
The composition in parts by volume of a sputtered lilm which was about 3 microns in thickness was This `ilm had a permeability of and a resistivity of 7 102 ohms-cm.
1. A sputtered granular ferromagnetic lm consisting essentially of a composition having the formula wherein x is from 0.001 to 0.7 part by volume and y is from 0.001 to 0.999 part by volume, and further characterized by having granular particle size on the order of 10 to 200 angstroms. v
2. A composition according to claim 1 wherein x is from 0.001 to 0.3 and y is from 0.10 and 0.60.
3,843,420 5 w e 3. A composition according to claim 2 wherein x is from References Cited O and y iS from tO 4. A composition according to claim 1 wherein x is from 7. An annealed film of claim 1.
s. An annealed fum of claim 2. 10 US' C1' X'R' 9. An annealed film of claim 4. 148-100; 204-192; 252-6259 10. A annealed film of claim 6.